Editorials

How summary measures of population health are affecting health agendas Paul J. van der Maas1

Summary measures of population health specific disability information should be second type of application is the assess- (SMPH) combine information on included. ment of the relative contributions of mortality and non-fatal health outcomes Most of these issues have ethical different diseases, injuries and risk factors to represent the health of a particular implications, and summary measures to overall population health. The world population in a single numerical index have also stirred up a lively debate on health report 2002 is a good example of such (1). Traditionally, mortality statistics empirical ethics. Choices in the construc- an application (3). The ultimate goal of have been the solid basis of population tion of SMPH implicitly or explicitly SMPH is to support policy decisions in the allocation of resources for prevention, health measures. They still are, but reflect underlying preferences. For health health care and research. For such priority as preventive and curative health care gap measures, such as DALYs, which express the burden of disease as a loss setting, information on the relative size became more effective at modifying of health with respect to a certain norm of health problems and risk factors is an disease patterns, morbidity became for population health, the choice of that indispensable part of the evidence needed. an indispensable population health norm value implies the health target for WHO’s recent publication on the indicator, especially in low-mortality that population. Health inequalities may ‘‘concepts, ethics, measurement and populations. Thus, since the 1960s there to a greater or lesser extent be reflected applications’’ of SMPH reflects the fact have been efforts to develop measures in a summary measure. Preferences for that nowadays, few will doubt whether that combine both types of information. investing in health in younger versus older summary measures of population health This has opened up a vast new age groups may be included in SMPH belong to the core methods of health research domain. Whereas mortality can by applying age weights. statistics (4). They are widely used for all be measured in a straightforward way and Although in practice the weakest area the purposes mentioned above. The occurs only once for each individual, in SMPH at the moment is the availability debate is not any more whether SMPH are the statistics involved are also relatively of reliable and comparable data on disease useful, but which ones are useful for a straightforward. For non-fatal health and disability, the choice of weights to given purpose. There is obviously no ‘‘one outcomes the opposite is the case. There relate disease and disability with mortality size fits all’’ solution for the development is a nearly infinite variety in definition and has probably caused the most heated and application of these measures. Neither measurement of such outcomes, each debate. The main issues concern whose will summary measures ever replace person will experience several of them values should be used (those of patients, more detailed reporting of health data. during their lifetime, and there are many professionals or the general public, and Perhaps the most important contri- different ways to aggregate such as seen globally or locally) and the bution of this methodology is not the information. valuation method to be used. Valuation end product, the summary measures The publication of the Global Burden methods differ with respect to the magni- themselves, but the way they force us to define the exact epidemiological input of Disease study by the World Bank in tude of the resulting weights. These needed regarding mortality and disability. 1993 was a landmark event in the SMPH will determine how much a specific In doing this they promote the application debate (2). For the first time, mortality summary measure will accentuate the of uniform classifications and the collec- and morbidity statistics for the world importance of morbidity and disability tion of missing information, calling for population were combined into one single relative to mortality. Fortunately, however, systematic checking of the internal summary measure for maximum the available empirical data show that consistency of epidemiological informa- comparability. The unit of measurement the ranking of most diseases and health tion on specific diseases. Thus, apart devised for this purpose was the states does not greatly vary between from their role in setting health care and disability-adjusted life year (DALY). The populations and cultures. Thus, in practice research agendas, they also set agendas for publication of this study stirred up a in the calculation of SMPH, sets of international comparative data collection lively debate on the methodological and disability weights can easily be replaced, and epidemiological research. n ethical aspects of SMPH. depending on the purpose of a specific The most important issues are: first, SMPH. 1. Field MJ, Gold MR, editors. Summarizing popula- the selection of health domains and the SMPH have a wide range of applica- tion health: directions for the development and measurement of health indicators within tions. They can be used to compare the application of population metrics. Washington (DC): National Academy Press; 1998. those domains; second, the calculation health of populations, to describe the 2. The World Bank. Investing in health. Oxford: Oxford of health expectancies such as ‘‘healthy life changes in health of a certain population University Press; 1993. expectancy’’, or rather health gaps, such over time, and to describe the distribution 3. The world health report 2002: reducing risks, as DALYs, where the present population of health within populations. In order to promoting healthy life. Geneva: World Health health is compared to a certain standard; make such descriptive applications useful, Organization; 2002. and third, the valuation of health states. the paramount requirement is that the 4. Murray CJL, Solomon JA, Mathers CD, Lopez AD editors. (2002) Summary measures of population Other issues concern the epidemiological measurement of the constituent parts health — concepts, ethics, measurement and approach (incidence versus prevalence of the SMPH is standardized and stable applications. Geneva: World Health Organization; measures) and whether generic or disease- between countries and over time. A 2002.

1 Professor of Public Health, Erasmus University Medical Centre, PO Box 2040, 30000 CA Rotterdam, Netherlands (email: [email protected]).

314 Bulletin of the World Health Organization 2003, 81 (5)